Question: Rosa is building a guitar. The second fret is $33.641\,\text{mm}$ from the first fret. The third fret is $31.749\,\text{mm}$ from the second fret. How far is the third fret from the first fret?
Distance from first to second fret $+$ distance from second to third fret $=$ total distance. $\begin{matrix} &&&&&\\ &{3}&3.&6&4&1\\ +&{3}&1.&7&4&9\\ \hline &{6}&5.&3&9&0\\ \end{matrix}$ ${30}+{30}={6}{0}$ The third fret is $65.39\,\text{mm}$ from the first fret.